Bake normals map does not work well
You should make your low poly model smooth shaded and add at least one bevel in this case. 

When blender bakes the normals, it ray casts from the low poly surface inwards along the interpolated normal until it hits the high poly (or not).

If you need the low poly to intersect with the high poly then you can make a copy of the low poly and scale (or shrink/fatten) it up and bake with that. It is also possible to use a Displace modifier to raise the surface a bit during the bake.